view src/hashtab.c @ 2894:fe9c7da98b5e v7.3.220

updated for version 7.3.220 Problem: Python 3: vim.error is a 'str' instead of an 'Exception' object, so 'except' or 'raise' it causes a 'SystemError' exception. Buffer objects do not support slice assignment. When exchanging text between Vim and Python, multibyte texts become gabage or cause Unicode Expceptions, etc. 'py3file' tries to read in the file as Unicode, sometimes causes UnicodeDecodeException Solution: Fix the problems. (lilydjwg)
author Bram Moolenaar <bram@vim.org>
date Sun, 19 Jun 2011 00:27:51 +0200
parents 6768ebd0bc04
children 2c12cd5c1381
line wrap: on
line source

/* vi:set ts=8 sts=4 sw=4:
 *
 * VIM - Vi IMproved	by Bram Moolenaar
 *
 * Do ":help uganda"  in Vim to read copying and usage conditions.
 * Do ":help credits" in Vim to see a list of people who contributed.
 * See README.txt for an overview of the Vim source code.
 */

/*
 * hashtab.c: Handling of a hashtable with Vim-specific properties.
 *
 * Each item in a hashtable has a NUL terminated string key.  A key can appear
 * only once in the table.
 *
 * A hash number is computed from the key for quick lookup.  When the hashes
 * of two different keys point to the same entry an algorithm is used to
 * iterate over other entries in the table until the right one is found.
 * To make the iteration work removed keys are different from entries where a
 * key was never present.
 *
 * The mechanism has been partly based on how Python Dictionaries are
 * implemented.  The algorithm is from Knuth Vol. 3, Sec. 6.4.
 *
 * The hashtable grows to accommodate more entries when needed.  At least 1/3
 * of the entries is empty to keep the lookup efficient (at the cost of extra
 * memory).
 */

#include "vim.h"

#if defined(FEAT_EVAL) || defined(FEAT_SYN_HL) || defined(PROTO)

#if 0
# define HT_DEBUG	/* extra checks for table consistency  and statistics */

static long hash_count_lookup = 0;	/* count number of hashtab lookups */
static long hash_count_perturb = 0;	/* count number of "misses" */
#endif

/* Magic value for algorithm that walks through the array. */
#define PERTURB_SHIFT 5

static int hash_may_resize __ARGS((hashtab_T *ht, int minitems));

#if 0 /* currently not used */
/*
 * Create an empty hash table.
 * Returns NULL when out of memory.
 */
    hashtab_T *
hash_create()
{
    hashtab_T *ht;

    ht = (hashtab_T *)alloc(sizeof(hashtab_T));
    if (ht != NULL)
	hash_init(ht);
    return ht;
}
#endif

/*
 * Initialize an empty hash table.
 */
    void
hash_init(ht)
    hashtab_T *ht;
{
    /* This zeroes all "ht_" entries and all the "hi_key" in "ht_smallarray". */
    vim_memset(ht, 0, sizeof(hashtab_T));
    ht->ht_array = ht->ht_smallarray;
    ht->ht_mask = HT_INIT_SIZE - 1;
}

/*
 * Free the array of a hash table.  Does not free the items it contains!
 * If "ht" is not freed then you should call hash_init() next!
 */
    void
hash_clear(ht)
    hashtab_T *ht;
{
    if (ht->ht_array != ht->ht_smallarray)
	vim_free(ht->ht_array);
}

/*
 * Free the array of a hash table and all the keys it contains.  The keys must
 * have been allocated.  "off" is the offset from the start of the allocate
 * memory to the location of the key (it's always positive).
 */
    void
hash_clear_all(ht, off)
    hashtab_T	*ht;
    int		off;
{
    long	todo;
    hashitem_T	*hi;

    todo = (long)ht->ht_used;
    for (hi = ht->ht_array; todo > 0; ++hi)
    {
	if (!HASHITEM_EMPTY(hi))
	{
	    vim_free(hi->hi_key - off);
	    --todo;
	}
    }
    hash_clear(ht);
}

/*
 * Find "key" in hashtable "ht".  "key" must not be NULL.
 * Always returns a pointer to a hashitem.  If the item was not found then
 * HASHITEM_EMPTY() is TRUE.  The pointer is then the place where the key
 * would be added.
 * WARNING: The returned pointer becomes invalid when the hashtable is changed
 * (adding, setting or removing an item)!
 */
    hashitem_T *
hash_find(ht, key)
    hashtab_T	*ht;
    char_u	*key;
{
    return hash_lookup(ht, key, hash_hash(key));
}

/*
 * Like hash_find(), but caller computes "hash".
 */
    hashitem_T *
hash_lookup(ht, key, hash)
    hashtab_T	*ht;
    char_u	*key;
    hash_T	hash;
{
    hash_T	perturb;
    hashitem_T	*freeitem;
    hashitem_T	*hi;
    int		idx;

#ifdef HT_DEBUG
    ++hash_count_lookup;
#endif

    /*
     * Quickly handle the most common situations:
     * - return if there is no item at all
     * - skip over a removed item
     * - return if the item matches
     */
    idx = (int)(hash & ht->ht_mask);
    hi = &ht->ht_array[idx];

    if (hi->hi_key == NULL)
	return hi;
    if (hi->hi_key == HI_KEY_REMOVED)
	freeitem = hi;
    else if (hi->hi_hash == hash && STRCMP(hi->hi_key, key) == 0)
	return hi;
    else
	freeitem = NULL;

    /*
     * Need to search through the table to find the key.  The algorithm
     * to step through the table starts with large steps, gradually becoming
     * smaller down to (1/4 table size + 1).  This means it goes through all
     * table entries in the end.
     * When we run into a NULL key it's clear that the key isn't there.
     * Return the first available slot found (can be a slot of a removed
     * item).
     */
    for (perturb = hash; ; perturb >>= PERTURB_SHIFT)
    {
#ifdef HT_DEBUG
	++hash_count_perturb;	    /* count a "miss" for hashtab lookup */
#endif
	idx = (int)((idx << 2) + idx + perturb + 1);
	hi = &ht->ht_array[idx & ht->ht_mask];
	if (hi->hi_key == NULL)
	    return freeitem == NULL ? hi : freeitem;
	if (hi->hi_hash == hash
		&& hi->hi_key != HI_KEY_REMOVED
		&& STRCMP(hi->hi_key, key) == 0)
	    return hi;
	if (hi->hi_key == HI_KEY_REMOVED && freeitem == NULL)
	    freeitem = hi;
    }
}

/*
 * Print the efficiency of hashtable lookups.
 * Useful when trying different hash algorithms.
 * Called when exiting.
 */
    void
hash_debug_results()
{
#ifdef HT_DEBUG
    fprintf(stderr, "\r\n\r\n\r\n\r\n");
    fprintf(stderr, "Number of hashtable lookups: %ld\r\n", hash_count_lookup);
    fprintf(stderr, "Number of perturb loops: %ld\r\n", hash_count_perturb);
    fprintf(stderr, "Percentage of perturb loops: %ld%%\r\n",
				hash_count_perturb * 100 / hash_count_lookup);
#endif
}

/*
 * Add item with key "key" to hashtable "ht".
 * Returns FAIL when out of memory or the key is already present.
 */
    int
hash_add(ht, key)
    hashtab_T	*ht;
    char_u	*key;
{
    hash_T	hash = hash_hash(key);
    hashitem_T	*hi;

    hi = hash_lookup(ht, key, hash);
    if (!HASHITEM_EMPTY(hi))
    {
	EMSG2(_(e_intern2), "hash_add()");
	return FAIL;
    }
    return hash_add_item(ht, hi, key, hash);
}

/*
 * Add item "hi" with "key" to hashtable "ht".  "key" must not be NULL and
 * "hi" must have been obtained with hash_lookup() and point to an empty item.
 * "hi" is invalid after this!
 * Returns OK or FAIL (out of memory).
 */
    int
hash_add_item(ht, hi, key, hash)
    hashtab_T	*ht;
    hashitem_T	*hi;
    char_u	*key;
    hash_T	hash;
{
    /* If resizing failed before and it fails again we can't add an item. */
    if (ht->ht_error && hash_may_resize(ht, 0) == FAIL)
	return FAIL;

    ++ht->ht_used;
    if (hi->hi_key == NULL)
	++ht->ht_filled;
    hi->hi_key = key;
    hi->hi_hash = hash;

    /* When the space gets low may resize the array. */
    return hash_may_resize(ht, 0);
}

#if 0  /* not used */
/*
 * Overwrite hashtable item "hi" with "key".  "hi" must point to the item that
 * is to be overwritten.  Thus the number of items in the hashtable doesn't
 * change.
 * Although the key must be identical, the pointer may be different, thus it's
 * set anyway (the key is part of an item with that key).
 * The caller must take care of freeing the old item.
 * "hi" is invalid after this!
 */
    void
hash_set(hi, key)
    hashitem_T	*hi;
    char_u	*key;
{
    hi->hi_key = key;
}
#endif

/*
 * Remove item "hi" from  hashtable "ht".  "hi" must have been obtained with
 * hash_lookup().
 * The caller must take care of freeing the item itself.
 */
    void
hash_remove(ht, hi)
    hashtab_T	*ht;
    hashitem_T	*hi;
{
    --ht->ht_used;
    hi->hi_key = HI_KEY_REMOVED;
    hash_may_resize(ht, 0);
}

/*
 * Lock a hashtable: prevent that ht_array changes.
 * Don't use this when items are to be added!
 * Must call hash_unlock() later.
 */
    void
hash_lock(ht)
    hashtab_T	*ht;
{
    ++ht->ht_locked;
}

#if 0	    /* currently not used */
/*
 * Lock a hashtable at the specified number of entries.
 * Caller must make sure no more than "size" entries will be added.
 * Must call hash_unlock() later.
 */
    void
hash_lock_size(ht, size)
    hashtab_T	*ht;
    int		size;
{
    (void)hash_may_resize(ht, size);
    ++ht->ht_locked;
}
#endif

/*
 * Unlock a hashtable: allow ht_array changes again.
 * Table will be resized (shrink) when necessary.
 * This must balance a call to hash_lock().
 */
    void
hash_unlock(ht)
    hashtab_T	*ht;
{
    --ht->ht_locked;
    (void)hash_may_resize(ht, 0);
}

/*
 * Shrink a hashtable when there is too much empty space.
 * Grow a hashtable when there is not enough empty space.
 * Returns OK or FAIL (out of memory).
 */
    static int
hash_may_resize(ht, minitems)
    hashtab_T	*ht;
    int		minitems;		/* minimal number of items */
{
    hashitem_T	temparray[HT_INIT_SIZE];
    hashitem_T	*oldarray, *newarray;
    hashitem_T	*olditem, *newitem;
    int		newi;
    int		todo;
    long_u	oldsize, newsize;
    long_u	minsize;
    long_u	newmask;
    hash_T	perturb;

    /* Don't resize a locked table. */
    if (ht->ht_locked > 0)
	return OK;

#ifdef HT_DEBUG
    if (ht->ht_used > ht->ht_filled)
	EMSG("hash_may_resize(): more used than filled");
    if (ht->ht_filled >= ht->ht_mask + 1)
	EMSG("hash_may_resize(): table completely filled");
#endif

    if (minitems == 0)
    {
	/* Return quickly for small tables with at least two NULL items.  NULL
	 * items are required for the lookup to decide a key isn't there. */
	if (ht->ht_filled < HT_INIT_SIZE - 1
					 && ht->ht_array == ht->ht_smallarray)
	    return OK;

	/*
	 * Grow or refill the array when it's more than 2/3 full (including
	 * removed items, so that they get cleaned up).
	 * Shrink the array when it's less than 1/5 full.  When growing it is
	 * at least 1/4 full (avoids repeated grow-shrink operations)
	 */
	oldsize = ht->ht_mask + 1;
	if (ht->ht_filled * 3 < oldsize * 2 && ht->ht_used > oldsize / 5)
	    return OK;

	if (ht->ht_used > 1000)
	    minsize = ht->ht_used * 2;  /* it's big, don't make too much room */
	else
	    minsize = ht->ht_used * 4;  /* make plenty of room */
    }
    else
    {
	/* Use specified size. */
	if ((long_u)minitems < ht->ht_used)	/* just in case... */
	    minitems = (int)ht->ht_used;
	minsize = minitems * 3 / 2;	/* array is up to 2/3 full */
    }

    newsize = HT_INIT_SIZE;
    while (newsize < minsize)
    {
	newsize <<= 1;		/* make sure it's always a power of 2 */
	if (newsize == 0)
	    return FAIL;	/* overflow */
    }

    if (newsize == HT_INIT_SIZE)
    {
	/* Use the small array inside the hashdict structure. */
	newarray = ht->ht_smallarray;
	if (ht->ht_array == newarray)
	{
	    /* Moving from ht_smallarray to ht_smallarray!  Happens when there
	     * are many removed items.  Copy the items to be able to clean up
	     * removed items. */
	    mch_memmove(temparray, newarray, sizeof(temparray));
	    oldarray = temparray;
	}
	else
	    oldarray = ht->ht_array;
    }
    else
    {
	/* Allocate an array. */
	newarray = (hashitem_T *)alloc((unsigned)
					      (sizeof(hashitem_T) * newsize));
	if (newarray == NULL)
	{
	    /* Out of memory.  When there are NULL items still return OK.
	     * Otherwise set ht_error, because lookup may result in a hang if
	     * we add another item. */
	    if (ht->ht_filled < ht->ht_mask)
		return OK;
	    ht->ht_error = TRUE;
	    return FAIL;
	}
	oldarray = ht->ht_array;
    }
    vim_memset(newarray, 0, (size_t)(sizeof(hashitem_T) * newsize));

    /*
     * Move all the items from the old array to the new one, placing them in
     * the right spot.  The new array won't have any removed items, thus this
     * is also a cleanup action.
     */
    newmask = newsize - 1;
    todo = (int)ht->ht_used;
    for (olditem = oldarray; todo > 0; ++olditem)
	if (!HASHITEM_EMPTY(olditem))
	{
	    /*
	     * The algorithm to find the spot to add the item is identical to
	     * the algorithm to find an item in hash_lookup().  But we only
	     * need to search for a NULL key, thus it's simpler.
	     */
	    newi = (int)(olditem->hi_hash & newmask);
	    newitem = &newarray[newi];

	    if (newitem->hi_key != NULL)
		for (perturb = olditem->hi_hash; ; perturb >>= PERTURB_SHIFT)
		{
		    newi = (int)((newi << 2) + newi + perturb + 1);
		    newitem = &newarray[newi & newmask];
		    if (newitem->hi_key == NULL)
			break;
		}
	    *newitem = *olditem;
	    --todo;
	}

    if (ht->ht_array != ht->ht_smallarray)
	vim_free(ht->ht_array);
    ht->ht_array = newarray;
    ht->ht_mask = newmask;
    ht->ht_filled = ht->ht_used;
    ht->ht_error = FALSE;

    return OK;
}

/*
 * Get the hash number for a key.
 * If you think you know a better hash function: Compile with HT_DEBUG set and
 * run a script that uses hashtables a lot.  Vim will then print statistics
 * when exiting.  Try that with the current hash algorithm and yours.  The
 * lower the percentage the better.
 */
    hash_T
hash_hash(key)
    char_u	*key;
{
    hash_T	hash;
    char_u	*p;

    if ((hash = *key) == 0)
	return (hash_T)0;	/* Empty keys are not allowed, but we don't
				   want to crash if we get one. */
    p = key + 1;

    /* A simplistic algorithm that appears to do very well.
     * Suggested by George Reilly. */
    while (*p != NUL)
	hash = hash * 101 + *p++;

    return hash;
}

#endif